Teletypewriter secrecy system



June 4, m

E. o. GAMMELL- 4 9 TELETYPEWRITER SECRECY SYSTEM Filed May 10, 1943 2 Sheets-Sheet l 1 INVENTOR E a Gu /mu ATTORNEY ZAMATg Jame 4,l%. E. o. GAMMELL TELETYPEWRITER SEGRECY SYSTEM 7 2 Sheets-Shegt 2 Filed May 10, 1943 MQN WEN

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. W EN INVENTOR" v EQGQIWI/IQQZZ ATTORNEY Patented June 4, 1946 UlTE TELETYPEWRITER SECRECY SYSTEM ApplicationMaylO, 1943, Serial No. 486,286

v 8 Claims. 1

This invention relates tosecrecy systems. More particularly it relates to telegraph and teletypewritersystem which arearranged for the. secret transmission of. signals.

It has heretofore been the practice in teletypewriter systems,,for example, to obtain some degree of. secrecy by specially arranging the sending; contacts and the receiving. code bars of the teletypewriter machines. In such prior secrecy systems-each teletypewriter signal or characterwhich usually includes: five marking or spacing pulses, in the ordinary Baudot code systeme-un- H dergoes a change. in. one of: its five pulses. For example, the second pulse. may be reversed at the transmitter from marking to'spacing or vice versa. This type of system is so arranged that a corresponding reversal in the changed pulse is caused to take place at. the corresponding code bars in the receiving; machine. so as to reproduce the .originalisignal or character.

In my application, Serial No.. 479,405, filed March 17-, 1943,.1 have. disclosed an arrangement to obtain secrecy by means of pulse reversals, thesereversals being produced by a simple circuit translation as distinguished from a mechanical change in the-teletypewriter units. Said applicationalso. disclose an arrangement tocause the pulse-reversals to be transferred from pulse to pulse of, the Baudot. code in a desired Order at successive-but unequal intervals. By this method the cipher. in accordance withwhich. the code is translated is. changed in an arbitrary andirregular: manner which renders itmore difiicult for an unauthorized person to-break the cipher.

Thepresent invention hasfor an object to encipher a1messagetby interchanging or transposing the. order of the pulses of the codeas distinguished from a cipher which involves 'a-mere reversal of one ormore of. the pulses. For example, instead of sending the pulses in 1--2-345 order, they may be sent in the order 24-531.

The order in which thepulses of the Baudot code. may be transmittedis.susceptible of many variations. Consequently by this plan a message may be. disguisedor concealed by employing a great many ciphers. By changing the order of the pulses: fromtimeto. time in accordance 'with aprearranged scheme,.0r, in accordance with instructions transmitted: by. the sending operator in code to the receivingoperator'from time to time, avery: high degree. of' secrecy may be obtained. Astillihigher. degree of secrecy may be obtained by not only making changes in the order of the pulses in accordance with the present invention, but in addition introducing pulsereversals by 2. means of arrangements such as those disclosed in my application, Serial. No. 479,405, already referred to. I

When. theswitching equipment for interchanging or transposing the order of the pulses at the sending station: is set ina particular manner, the corresponding; equipment at the receiver cannot be set to transpose the order of the pulsesin the same manner, but must be set toproduce an inverse change in the order of thepulses. This will restore the individualimpulses of'theBaudot code to their. original order at the receiver. For example, if the pulses are sent in the order. 24-- 5--31 at the sending station, the translation of pulses is from 1 to 2, 2 to 4; 3 to5, 4 to 3 and 5 to 1. At the receiving station the translation must be from 2. to 1,4 to 2,. 5 to: 3, 3 to 4- and l to 5; in order to restore the original order 1--2' 3-45.

The invention may now be more fully understood from the following description of the apparatuswhen read in connectionrwith the accompanying drawings. In the drawings Figure 1 shows the apparatus to be used at a transmitting station for enciphering the message, it being understood that similar apparatus will be used at the receiving, station for deciphering purposes. Fig.2 is a schematic layout ofi'a line circuit having, enciphering. arrangements of the type shown in'Fig. 1' at both the transmitting and receiving stations. Fig. 3 shows a modified arrangement of the apparatus to be used at the transmitting station tointroduce pulse reversals as well asv to transpose the order of the pulses; Fig. 4 is a schematiclayout ofa linecircuit having enciphering arrangements ofthe type shown in Fig. 3 at both the transmitting and receiving, tations.

Referring to Fig. l, the circuit at the transmitting station includesia distributor D'of the type usedinstart-stop teietypewriter systems. said distributor having a start segment, fiveBaudot pulse segments and; a stop egment over which a brush B may rotate. Whenthe apparatus is'set into operatiomthe brushB at thev sending station may rotatecontinuously. The brush of the correspondingsegment in the receivingprinter, however, rotates intermittently, being started by the start impulse sent'out by the transmitting distributor, and stopped fora brief interval when the stop impulse is received;

A tape transmitter of the type commonly used in teletypewriter circuits is shown schematically at TT and includes five transmitting contacts,

T01, TCz,,TC3, T04 and-T'C's by means of which marking. or spacing impulses. may be applied to responding to each contact of the tape transmitter TT.

As will be evident from Fig.1 of the drawings, the contacts of the tape transmitter TT are individually connected to the several conductors 1, 2, 3, 4 and 5. Correspondingly conductors 2|, 22, 23, 2'4 and 25 lead from the segments 1, 2, 3, 4 and 5 of the distributor D. The keys are so arranged that any one of the conductors I, 2, 3, 4

' or 5 may be connected to any one of the condu'ctors H, 22, 23, 24 or 25. Normally the conductors I-5, inclusive, are connected to the conductors 21-25, inclusive, in numerical order. If the conductors were normally disconnected from each other, it would require twenty-five keys arranged in five horizontal and five vertical rows to cross-connect the conductors in all of the possible combinations. Since, however, the conductors are normally connected together as above'stated, and each key is arranged to break one of these normal connections, only four keys in each horizontal or vertical row are required, so that a total of twenty keys will make all of the cross-connections possible.

The keys are all designated by the letter K preceded by a number 21, 22,- 23, etc., corre,

sponding to the distributor connections 2|, 22, 23, etc., with which the several vertical groups of keys are associated. The letter K designating the keys is followed by subscripts such as l, 2,3, 4 and 5, corresponding to the conductors l, 2, 3, 4 and 5 leading to the contacts of the tape transmitter TT. Thus the keys 2'|K2, 2 IK3,

2IK4 and ZlKs in the upper horizontal row are all connected in the conductor 2| and serve individually to disconnect said conductor from conductor 1 leading to the contact TC]. of the tape transmitter and connect it to one of the horizontal row is connected to the lower key of one of the Vertical rows. For example, the last key ZlKs of the first horizontal row is connected by conductor 2H to the lower key 25K1 of the first vertical row. In this vertical row all of the keys have the subscript 1. Likewise the last key 22115 of the second vertical row is connected by means of the conductor 222 to the lower key 25K2 of the second vertical rowin which the keys all have the subscript 2. So also key 23K5 is connected by conductor 233 to key 25K3, and conductor 244 connects keys 2'4K5 and 25K4;

By means of these connections a, circuit may be normally traced from the first segment of'the distributor D, over conductor 2!, over the normal 12 contacts of the keys 2|K2 to ZlKs, inclusive, in the first horizontal row, thence over conductor 2| I, over the normal a contacts of the vertical row of keys 25K1 to 22K1, inclusive, and thence over conductor I to the contact T01 of the tape transmitter TT. Similarly segment 2 of the distributor is normally connected over the normal Z2 contacts of the keys 22811 to 22K5, inclusive, in the second horizontal row, thence over conductor 222, over normal contacts a of the keys 25K2 to 2 IK2 in the second vertical row, and thence over conductor 2 to contact 'I'Cz of the tape transmitter. Likewise normal connections may be traced from the third, fourth and fifth segments of the distributor D to the con tacts TCs, TC4 and T05 of the tape transmitter TT. For example, the latter connection extends over conductor 25, thence over the normal b contacts of the keys 25K1 to 25K4, inclusive, in the fifth horizontal row, thence over the conductor 255 and over the normal a contacts of the vertical rows of keys K5 to 2|K5, inclusive, in the last vertical row, and thence over conductor 5 to contact TCE; of the tape transmitter.

With the circuits in the condition above described, the impulses set up by the contacts TCl-TCs, inclusive, of the tape transmitter TT will'be transmitted in the order of "their subscripts from the segments 1, 2, 3,4 and 5 of the distributor D to the line L. If the contact TC], is in its normal or spacing condition, an open circuit impulse will be transmitted. If, however; contact is shifted to the left, which is its marking condition, battery will be transmitted over conductor 40 and over segment 1 of the distributor to the line L as the first impulse of the Baudot code. The second'impulse will be either an open circuit impulse or a marking impulse from the contact'TCz, dependingwhether the contact is in its normal position or has been moved to the left. The characters represented by the Baudot code combinations will, therefore, be transmitted in their .normal code arrangements in non-ciphered form.

Suppose now it is desired to transpose the code combinations from their unenciphered form in which they are transmitted in the order 12 345 to some enciphered order. For example, let us assume that it is desired to interchange the order of the pulses to 24-5-3-1. The first horizontal row of keys determines which of the contacts of the tape transmitter TT is connected'to the first segment of'the distributor. Similarly the second horizontal row of keys determines which contact of the tape transmitter is connected tothesecond segment of the distributor, etc. To transmit the pulses in the order 245-3l, the key having the subscript 2 in the first horizontal row, that is key 2IK2, will be thrown. Similarly key 22K; in the second row, key 23K5 in the third row, key 24K3 in the fourth row and key 25K1 in the fifth row will be thrown.

With this arrangementof keys segment 1 of the'distributor will be connected over conductor 2|, make contact a of key 2 lKz and over conductor 2 to the contact T02 of the tape transmitter. Therefore, the first pulse transmitted will be that from the contact 'ICz. Similarly segment? of the distributor is connected over conductor 22, over the normal I) contacts of keys 22K1 and 2'2K3, over the makea contact of key 22K4, over normal 0. contact of key 2 [K4: and over conductor 4 to the contact T04 of the tape transmitter, so that the second pulse transmitted'will be the fourth pulse set up on the tape transmitter.

- Segment 3 of the distributor is connected over the normal b contacts-of 'keys 23K1,23Kz and 51 23K4, overmake contact a of key 23K5, over-the normal 12 contacts of keys- ZZK-kahd ZlKs, and thence over conductor to" the. contact T05 of: the tape transmitter. Segment l-of the distributor is connected overconductor 24, normal 7) contacts of keys 24K1 and 24m, make a contact; of key 25K3, over normal (1 contacts-of keys .2-2K'a and 2|K3, and thence over conductor 3-to"con'-- tact TC; of' the tape transmitter. Finally'segment 5 of the distributor is connected over conductor 25', make a contact of key 25Ki, over the. normal (1. contacts of ZLiKi, 23K1 and" 22K1, and thence over conductor l to the contact TC1 of the tape transmitter. Thus itwilli beseenxthat' the pulses set up on the tape transmitter will be transmitted from the tape contacts in: the following order: T02, TC i, T05, TCs and T01.

The manner in which the transposedor interchanged pulses of the Baud'ot code are transmitted to a receiving station over the line L and how: they are utilized at the receiving station to decipher the message is as follows: In Fig. 2 the message is applied by means of a tapeT to. the transmitterTTi which corresponds. to the transmitter T of Fig. l. The pulsesare. theninterchanged in order by means of the mixing. apparatus MXD1 which corresponds to the apparatus MXD of Fig. l. The interchanged pulses are then transmitted. over the line L and: applied to a reperforator PRFZ which perforates a tape T2 in which the code combinations will appear in their transposed form.

The code combinationsthus appearing. in enciph'ered form upon the tape. T2 are applied: to the. tape-transmitter TT2;WhlCh is similar to the transmitter T1 of Fig; 1. The impulses setup; on the transmitter are then applied to the mixing or interchanging apparatusMXDz, which is similar to that of. Fig. 1. It operatesas' will be explained presently, to restore the. order of the impulses of each code combination to'its'normal form, so that when applied to a teletypewriter such as that shown symbolically at TTY2, the original: message will be printed upon the teletypewriter.

The setting of the-mixin apparatus MXDz at the receiving. station. will not be identical with that at the transmitting station, but will bein inverse relation thereto. It will be remembered that at the transmitting station, order to transmit the pulses l--2-3l'5 in the order 2-4--53--1, the keys HKZ, 22K4, 23K5, 24Ks and 25K1 where operated in the first; second, third,,fourth and fifth rowsof keys, respectively. In order to restore the pulses to their normal 12--345 order, it is necessary at the receivingstation to throw the key ElKs inthe first horizontal row, the key 22321 in the second horizontal row, the key 23K; in the third horizontal row, the key 24K2 in the fourth horizontal: row and the key 25K3 in the fifth horizontal row. This is because the first pulse'ofthe codeislset up on contact TCs at the receiver, the second pulse on TC1, the third pulse-on TC4, the fourth pulse on TCz. and the fifth pulse-on'ICs.

It will beseen by tracing thecircuits that this setting of the keys will restore the impulses of each Baudot' code to their normal order. Bearing. in mind that'the first impulse of the message character to be transmitted was thansmitted as the fifth impulse it will be set up on the contact corresponding to TCs on the tape transmitter T'I-z at the receiving. station. Therefore, when the brush of the distributor corresponding to D of the mixing apparatus MXDz at the receiving station passes over itsfirstsegment; a circuit-may betraced from the contact. TCeof the tape transmitter, over the conductor: 5,. over: make contact a1 of. key ZIKs; and thence over: normal: or con.- tacts of keys. 2lK4, 2IK3 and ZJKZ; to conductor 2| from which point the circuit passesv through the distributor and: over a conductor corresponding' to the line L of Fig. 1. tov th'eteletypewriter TTYz. Therefore an impulse corresponding to the original first pulse of the; unenciphered Baudot; code: is transmitted to the teletypewriter.

Inasimilar manner, bearing in. mind that the original second impulse of the; unenciphered Baudot. code was transmitted. asv the. first. pulse, and noWappears-on: the contact. TC1 of. the tape transmitter. TT2 at the receiver. The. passing'of the brush ofthe distributor oven the second segment establishesthe following circuit; from the second segment; of the distributor, over-conductor. 22; over the make contact a ofkey. 22K1, and; over conductor 1 to the contact TCi of the tape trans:- mitter TF2. The impulse which was originally the second impulse of the unenciphered codeis; therefore, transmitted over the second segment of the distributor to the teletypewriter TTY-z. Similarly by tracing the circuits from-the other third, fourth and fifth segments of the distributor, it will be seen that all of the pulses in their enciphered form are; retransposed to their original positions. so that the character originally set up at the transmitting station will be received upon the receiving teletypewriter-'ITYZ;v

Fig. 3 shows how a transp'osing arrangement such as that illustrated in Fig. 1. may be combined with a pulse-reversing arrangement such as shown in my application; Serial No. 479,405, filed. March 17, 1943. shown on the left in Fig. 3 and designated MXD is identical with the apparatus bearing the same designation in-Fig-. 1". Likewise the tapetransmite ter TT in Fig. 3 is identical with that shown. in Fig. 1. However, the connections for applying marking or spacing potentials to the contacts of the. tape: transmitter TT are arranged in Fig. 3 to pass through: a. switching: apparatus. designated SE which will be described" in more: detail later: The switching apparatus SE is. controlled. as will appearhereinaftenzby a local: teletypewriter TTY. connected inthe line L..

Theswitching'apparatus SE includes'five pairs of transfer relays such as-TR1-TR.-1', TRz-TRa', etc., one pair correspondingto'. each pulse: of the Baudot code. Associatedwitheachpair of transfer relays is. astartingtkey: The keyassociated with the. pair of relays TR1.TR1. is shown at SKi, and similarly thestartingkeysfor the other pairs of transfer relaysa-re. shown at SKz, SK3,.SK4 andl 8K5, respectively.

By operating any particularly starting: key as, for example, the; starting. key SK2-, the corre sponding pair of transfer relays The and The is operated and. locked. up to'reverse the correspending-pulse of the Baudotcode, which in this case is: the second pulse. These relays will remain locked up until, as will be described later, the Baudot code-combination for figures. shift is sent to the line. L..-fr0m the distributor D followed'by the code combination of; some predetermined letter such, forexampla. as the letter S or the letter H. When this condition occurs, the teletypewriter mechanism. 'ITY will, immediately after the S combination has been transmitted, momentarily. open the contact Cx to unlock the previously operated pair of. transfer relays. The release. of these. relays. causes. the next pair of The mixing. apparatus transfer relays to be operated in turn.. Inthe case assumed the next pair of transfer relays will be the relays TR: and 'I'Rc' which, when energized and locked up, will cause the third impulse of each Baudot code to'be reversed-until such time as another figures-S combination occurs, whereupon the control'is transferred to the fourth pair of transfer relays to reverse the fourth impulse of the code, etc.

When the fifth pair of transfer relays TRfi- TRs' is operated in turn to reverse'the fifth impulse, the ensuing figures-S combination will release the fifth pair of transfer relays and transfer the control to the first pair of transfer relays TRi-TR1. Thereafter the control is successively passed through the various pairs of transfer relays again. The shifting of control from one pair of transfer relays to another occurs at irregular intervals determined by the fortuitous occurrence in the enciphered message of the fi ures-S combination. As an unauthorized person tapping .the line cannot know in advance when such a combination will occur, he would have no way of knowing that the cipher had been changed. This, of course, tends to render it much more difficult to break the cipher.

Associated with each pair of transfer relays is a transfer key such as the key 'I'Ki associated with the first pair, the transfer key TK2 associated with the second pair, .etc.- By operating any one or more of these transfer keys the corresponding pair or pairs of transfer relays will be effectively eliminated from the chain. Under these conditions the succession of controls will pass only through the pairs of transfer relays whose transfer keys are not actuated.

It is also possible to reverse more than one impulse of the Baudot code at a time. For example, if instead of starting the enciphering process by operating the key SKz, the starting keys SK1 and SK3 are simultaneously operated, the pairs of transfer relays TRi-TRl' and TR3TR3 will be simultaneously energized and locked up to reverse the first and third impulses. As soon as a figures-S combination occurs, however, these two pairs of transfer relays will be released and the second and fourth pairs of transfer relays will be actuated, these in turn being followed by the third and fifth pairs. After these are released by the ensuing figures-S combination the control will be transferred to i the fourth and first pairs,.the control later pass ing to the fifth and second pairs, etc.

Instead of using the transfer relays to reverse impulses, this effect may be accomplished by actuating any one or more of the lock-in pulsereversal keys PRKl-PRKS, inclusive, as will be described later. When the pulse reversal keys are used to reverse impulses, and it is desired to shift the reversal to other impulses, the transmitting operator must notify the receiving operator in code what keys are to be used to effect the shift. Before the lock-in pulse-reversal keys are used, any transfer relays which may have been previously operated and locked up are restored to normal by operating a clear-cut key OK.

The details of the circuit arrangement of Fig. 3 will be clear from the following description of its operation. Let us assume first that none of the keys of the apparatus MXD is operated, and that no one of the five sets of transfer relays of the switching apparatus SE is operated. Also assume that none of the pulse-reversal lock-in keys PRKl-PRKfi of the switching apparatus SE is operated. It will be evident that under these 2i and I to the tape, contact T01.

8 conditions the message will be transmitted in normal code combinations without being enciphered by any pulse reversals or by any transposition of pulses.

For example, as the brush arm .8 of the distributor D in Fig. 3 passes over its No. 1 segment,

the conductor 2| will be connected through keys of the mixing apparatus MXD to the conductor I, as described in connection with Fig. 1. Therefore, the line L will be connected over the inner ring of the distributor and over said conductors If the first pulse is a spacing pulse, the tape contact TCl will be in its right-hand position and-the circuit will be continued over said contact andover the normal contact of spring a of key PRK to the front contact of armature c or relay TR1. As the relay TR1 is not energized, the front contact of said armature c is open, and consequently an open circuit pulse is transmitted to the line. If, however,the first pulse of the code combination is a marking pulse, the tape contact TC1 will be in its left-hand position and the circuit will be extended over the normal contact of spring b of key PRK1, over the back contact of armature c of relay TR1 and thence over conductor 40 'to battery. Under. these conditions a marking impulse is transmited to the line L. The first pulse is consequently not reversed.

Similarly, as the brush passes over the second segment of the distributor, if neither the transfer relay TRz nor the key PRKz is actuated,.an open circuit will be transmitted to the line when the tape contact TCz is in its right-hand or spacing position, whereas if it is in its left-hand or marking position, battery will be connected to the line. Hence the second impulse will not be reversed. Likewise, under the conditions as-' sumed, theremaining pulses are also set normally and in regular order.

If it is desired to encipher the message by pulse reversals, the operator may cause the first pulse to be reversed by operating the start key 8K1,

normally closed contact of clear-out-key CK,

through the lamp L and over the contact Cx of the teletypewriter TTY to ground. When thus actuated, relays TR1 and TR1' are locked up in series over the front contact of the armature b of relay TR1, said locking circuit extending over the circuit above traced to ground at the contact Cx of the teletypewriter TTY.

Under these conditions, if the tape contact T01 is in its right-hand position, as would be the case when" the first pulse of the enciphered Baudot code is a spacing pulse, the circuit from the first segment of the distributor (if the apparatus-MXD is not set to transpose pulses) will be extended over the right-hand contact of tape contact T01, over the normal contact of spring a of key PRKI, over the front contact of armature c of relay TR1 (which is now pulled up), and thence over conductor 40 to battery. Thus a marking impulse will be transmitted to the line instead of a spacing impulse. If, however, the tape contact TCl is in its left-hand or marking position, the circuit from the first segment of the instead'of a marking pulse is sent to ithfi lineL. If no other pairs oftransfer relays are operated, the other four pulses of each Baudot codeare sent outunreversed.

Of course, if .keys of the mixing apparatus M29) are operated to transpose the pulses, the connections'abov described for the first pulse may be :switched :to some other segment of the distributor D instead of the first segment. For example, if pulses are transposed from theorder l23--45 to the order 2- i53-1,.a-S p viously described, the switch -25K1'in the fifth horizontal'row of mixing apparatus 'MXD will' be actuated. Consequently the conductor I will be connected through the switch -25K1 and over the .conductor .25 to .the fifth segment of the distributor D, Therefore, the reversed firstpulseset up on the tape transmitter T by the actionof the transfer relays TRi and TR1 will not be the first pulse transmitted by the distributor, but will be the last one. Indeed, under the'ccnditions-above described, the-first pulse transmitted by the-distributor D will be the pulse set up on thecontact T02 of the tape transmitter TT, This pulse will not be reversed unless the second set of transfer relays .is actuated, or the lock-in pulsereversalkey PRKs is thrown.

From the foregoing it will be seen that when both the mixing apparatus vMXD and'the switching equipment SE are used "shnultaneously, -the apparatus MXD transposes the order of the pulses-and in addition at .least one of the transposed pulses is reversed, .either b the setting-of one of the pulse-reversal keys ofthe PRK series,

or by the operation of a pair of transfer relays such as TRi and TRi. Consequently the character transmitted from the distributor D to the line L will not be the character punched on the tape which operates the tape transmitter T-T, but will be some othercharacter,dependingupon the crderin which the pulsesrare transmitted by the apparatus MXD, and upon which of thetransposed pulses is at anyparticulartime reversed.

Assuming that, as above-described, the transfer relays TRI aIIG. TRi were actuated and the keys of .the apparatus MXDset totranspose the order of the pulses as .described in connection with Fig. 1, successions of codecombinations'enciphered in accordance with the setting of the switching equipmentSEand the apparatus MXD will continueto be transmitted .to theline L until .the setting ischanged, When in the course of the message, the combination figures-S is transmitted to the line, the contact CX will be .momentarily opened .by the teletypewriter TTY, as described in connection with .Fig. 1. This combination is not necessarily the signal combination set up on the transmitter TT, but is usually some other combination of successive characters, translated by the setting of the switching equipment SEand the mixing apparatus MXD into the-code combinations f or figures-S.

Upon the momentary opening .of the switch -Cx in response to this combination, the .relays TRI and TRlwillbe released and the neXt-pair-ofrelays IE2 and TR2' will be operated and locked up, thus .in turn reversing the second impulse of each code combination setup onthe tape transmitter T1. The circuit .for operating the relay TRz passes :over the back contact .of :armature .a of .relay TR1, over th -frontcontact of slow-re- .lease relay TRi', over the normal contact of transferikey TKz, and through the winding of relay TRz to battery. Relay 'IRz, .at the frontcontact of its armature .b, completes-a locking cirrelays is released in response to a combination, the third pair will -.be energized to reverse the impulses set up on contact TC3,.and

=cuit through its own Winding and through the winding of the relay .TRZ', and thence over the contactof clear-out key CK to ground over the contact CX.

The impulse set up on the'contaot T02 of the tape transmitter TT. is now reversed, but under the conditions above assumed, this impulse will not be transmitted as the second impulse but as the first impulse, due to the actuation of the key ZlKz which connects the first segmentof the distributor D to the contact T02 in a manner already described in connection with the similar equipment of Fig, 1. Similarly, as successive pairs of transfer relays are energized and locked up when ,preceding transfer .relays are released, other pulses will be reversed.

For example, when the second pair of transfer ngures-S when the third pair is released by another figures-S-co-mbination, the fourth-pair will be energized to reverse the pulses set up on the con- .tact T64.

=ture a of the .rela TRs, overthe front contact of slow-release relay 'IRs, over the conductor 32,

.over the normal contactof transfer .key 'I-K1,-and

.throughthe windingof relay PR1 to battery. Re- .lay TRI is thus energizedand locks up in series with relay .T'R1 toagain reverse thefirst impulse of the Baudot code. This condition continues until the .neXt figuresesVsignal. is received, when the control isshiftedto the .nextipair of transfer relays and the cycle .is repeated.

As described in my .copendingapplication, .Se- .rial No. 479,465, filedMarch 17,.19d3,.any'desired pair .of transfer relays may be eliminated from the chain by operating the corresponding transfer key. For example, if :it .is desired to eliminate the transfer relays T32 and TRz'from the chain, the transfer .key TKz is operated to its right-hand position. Consequently, when'the relay TRi is released in response to a figures-S combination, a circuit is completed over -the back contact'of armaturea of relay TR1, front contact of slow-releasing relay TR1',.ov.er .the right-hand contact of key .TKz, over the left-hand contact of key TKs, through the winding of .relay TRs to battery. Relays TRs and TRs' are energized andlocked up, and relays TRz and 'IRz. are omitted from the'chain, so thatthe second'pulse will not be reversed. In a similar mannentany other pair of transfer relays may be eliminated from the chain, and if desired, more than one pair may be eliminated simultaneously by operating the .proper transfer keys.

Theswitching equipment SE.may be used to reverse :more than one pulse .in each code combi nation. For exam.ple,.if the .start keys SKz and SK; areoperatedsimultaneously, relays TRz and TRz willbe energizedland locked up over obvious circuits, and at the same time relays TR; .and TRA' will :be energized .andJocked up. This will result in reversing the second and fourth pulses of the Baudot code. If thepulses are also transposed by the mixing apparatus MXD as above described .so that the order of the pulses is changed from 12345 to the order 24 31, the first segment of the distributor will be connected to conductor 2, and consequently the first pulse transmitted to the line L will be reversed, although this pulse corresponds to the reversed second pulse of the original Baudot combination. Likewise the second segment of the distributor will be connected to conductor 4 in a manner previously described, and, therefore, the second pulse transmitted to the line L will be reversed, although this pulse actually corresponds to the reversed fourth pulse of the Baudot code. The third, fourth and fifth pulses transmitted to the line will correspond respectively to the fifth, third and first pulses of the Baudot code, as already described, but these pulses will not be reversed.

When, however, in response to a figures-8 combination the contact Cx is momentarily opened, the locking circuit for the pair of relays TRz and TRz' and the locking circuit for the pair of relays TR; and T34 will be opened, causing the release of these two pairs of relays. Relay TRz upon releasing cause the relays TR3 and TRB to operate and lock up. At the same time relay TR4 upon releasing causes the relays "IE5 and. 'I'Rs' to operate and lock up. This reverses the third and fifth pulses of the original Baudot code. With the mixing apparatus MXD set, as already described, the third reversed pulse will be transmitted to the line L as the fourth pulse and the fifth reversed pulse of the original Baudot code will be transmitted to the line L as the third pulse.

It will be, of course, evident that when the next figures-S combination occurs, the relay 'IRa upon releasing will operate and lock up the fourth pair of transfer relays to reverse the fourth pulse of the Baudot code, while the relay TRs unon releasing will operate and lock up relays TRi and TR1 over a c rcuit previously traced, thereby reversing the first pulse. It will thus be evident that the control is transferred from time to time through the chain of transfer relays two at a time, the next succession being the fifth and second pairs, then the first and third pairs. etc.

The manner in which the apparatus shown. in Fig. 3 operates at the transmittin station is indicated symbolically at the left-hand of Fig. 4. Here the switching equipment SE1 operates on the tape transmitter TT1 to reverse certain pulses of the tape T1 fed into the transmitter. The five pulses of each Baudot code with certain pulses thus reversed are in turn fed into the mixing apparatus MXD1, which transnoses the pulses in accordance with the setting of its keys. The code combinations thus enciphered are then transmitted through the teletypewriter T'IY1 to the line L. Whenever a figures-S combination is received in the telet pewriter T'I'Yi, it operates the contact Cx to shift the control of the transfer relays of the sw tching equipment SE1 to reverse different pulses of each Baudot code.

The enci hered codes are transmitted over line L to the receiving station, w ere they are applied to two renerforators RPFz and RPFz' of known type. These machines perforate two tapes T2 and T2. respectively. in accordance with the enciphered code combi ations. The tape T2 is fed into a ta e transmitter TT2' to operate a teletypewriter T'I'Yz' in accordance with the enciphered code. Whenever a figures-S combination is recorded on the teletyoewriter TTYz, it momentarily opens the contact Rx to shift the control by means of the switching equipment SE2 to the next set or sets of transfer relays It Will 12 be understood, of course, that the operation of the contact Cx atthe sending station has at that station caused a similar shift of the transfer relays in the switching equipment SE1. Thus when a shift in the pulse to be reversed takes place at the sending station, a similar shift occurs at the receiving station. The result of this is that the pulse reversed at the transmittin station is always rereversed or restored to normal at the receiving station.

It remains to be seen how the pulses transposed by the mixing equipment MXDr at the transmitting station are retransposed by the similar equipment MXDz at the receiving station. Whenever the operator at the transmitting sta tion sets the keys of the apparatus MXDI to transpose the order of the pulses in a particular manner, information is transmitted in code form to the receiving operator so that the receiving operator may set the keys of the apparatus MXDz to cause a reversed transposition of the pulses. This reversed transposition will be accomplished in the manner already described in connection with the mixing apparatus MXD2 in Fig. 2.

It will be seen, therefore, that the tape T2,

which is perforated in accordance with the enciphered code, will operate the contacts of transmitter TT2 in accordance with said code. The

transfer relays of the switching equipment SE2 operate to restore to normal any reversed pulses set up on the tape transmitter TT2. Also such pulses as are transposed will be retransposed to their original order by the apparatus MXD-i. Consequently the code combinations will be transmitted in unenciphered form to the recording teletypewriter TTY2. The teletypewriter TTY2, therefore, prints the message as it was originally set up on the tape T1.

It will be understood, of course, that if the. switching equipment SE1 at the sending station is set to reverse certain pulses by the operation of pulse-reversal keys such as PRK1, etc., the switching equipment SE2 at the receiving station will have its pulse-reversal keys set accordingly. Information may be transmitted in code from the transmitting operator to the receiving operatoras to how the pulse-reversal keys of the switching equipment SE2 must be set.

It will be obvious that by combining a system of pulse-reversals with a system of pulse transpositions as above described, it will be very difiicult for unauthorized persons to decipher the message by tapping the line. It will also be clear that when desired either the pulse-reversing equipment SE or the pulse transpositionequipment MXD maybe used separately. Thus by using the pulse-reversal equipment SE without setting any of the keys of the transposition equipment MXD, the message will be enciphered by merely reversing certain pulses. on the other hand, by setting certain keys of the transposition equipment MXD without operating any of (5 1. In a secrecy system, means to translate messages into combinations *of impulses representing characters or other signals in accordance with the Baudot code, means to encipher said code combinations by 'transposing the order of the pulses of each Baudot code, means to further encipher said code combinations including devices individual to eachof the five pulses comprising the Baudot code and capable when operated of reversing the-corresponding pulse f each code combination before it is'transmitted, "means causing any desired one of said devices to -:reverse'the pulse controlled byit in all of a number of successive code combinations, thereby enciphering a message or part thereofin one form, and means responsive each time certain Baudot code combinations "occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession to cause another pulse reversal in 'a different number of successive code combinations.

2. 'Inasecrecy-system, means to'translate'm'essages into combinations of impulses representing characters or other signals in accordance with the Baudot code, means to encipher said code combinations by transposing the order of the pulses of each of a succession of such Baudot codes'in the'same mannen-means to further encipher said code combinations including devices individual to each of the Two pulses comprising the Baudot code and-capable when operated of reversing the corresponding pulse of each code combination before it is transmitted, means causing-any desired one of said devices to reverse-the pulse "controlled by it'in all of a number of successive code combinations, thereby enciphering a message or partthereof in'one form, andmeans responsive each'tim'e certainBaudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of "said devices in succession to cause another pulse-reversalin-a different number of successive code combinations.

3. In a secrecy system, meanstotranslatemea sages into combinations of impulses representing characters or other signals in accordance with th Baudot code, means to encipher said code combinations by transposing the order of the pulses of each Baudot code, means to further encipher said code combinations including devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each code combination before it is transmitted, means causing any desired one of said devices to reverse the pulse controlled by it in all of a number of successive code combinations, thereby enciphering a message or part thereof in one form, means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession to cause another pulse reversal in a different number of successive code combinations, means to transmit the code combinations thus enciphered, means at a receiving station to restor the pulses of each received code combination to its original order, and means at each receiving station to restore the reversed pulses to normal.

4. In a secrecy system, means to translate messages into combinations of impulses representing characters or other signals in accordance with the Baudot code, means to encipher said code combinations by transposing the order of the pulses of each of a succession of such Baudot codes in the same manner, means to further vencipher said code combinations including devices individual to each of the five :pulses comprising theBaudot code :and capable whenoperated of reversing the corresponding pulse of each code combination before it is transmitted, means causing any desired'one of-said devices to reversethe pulsecon'tro lled by it in all-of "a number of successive code combinationsthereby enciphering a message or part thereof in one form, means responsive each time certain Baudot code combinationsoccur to-defeat control'by a previously operated device and totransfer'pulse reversal control toother of said-devices in succession to cause zanoth'er pulse reversal in a different number of successive-code combinations, :means to transmit the code combinations thus .enciphered, means at a receiving station to restore 'the pulses of --each;received acode combination to its original iorder, and means at each receiving station to irestoretthereversed pulsestonormal.

'5. .In a .secrecy.:system,.z.meansfto translate mes- :sages into combinations of .impulsesrepresenting characters or other 's'ignalszin accordance with the Baudot :code, Jsaid means .iincluding a transmitter :having contacts individual to each pulse of a sBaudot code combination and'to which said pulses may be :applied, .a distributor having segments for each pulse of :a'lcode combination tosucces- -sively transmit :sai'd pulses, means adapted to connect the individual segments of said distributorto'the individual "contacts of said transmitter, :means ito l-Shlft :said connections at will to encipher said .CO'dG combinations byitransposing the order invvhich :thepulse are transmitted, :means to further encipher ssai'd :code combinations including devices individual to each .of the five 513111865 comprising the Baudot code and capable when .operated of reversing the corresponding pulse of each .codexcombinationbefore it is transrmittedytmeans causing :any desired one of said idevicesltoireverse the pulse controlled-by it in all -:of :a number :of :successive code combinations, :thereby enciphering 1a [message or part :thereof in one form, and means :responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession to cause another pulse reversal in a dilferent number of successive code combinations.

6. In a secrecy system, means to translate messages into combinations of impulses representing characters or other signals in accordance with the Baudot code, said means including a transmitter having contacts individual to each pulse of a Baudot code combination and to which said pulses may be applied, a distributor having segments for each pulse of a code combination to successively transmit said pulses, means adapted to connect the individual segments of said distributor to the individual contacts of said transmitter, means to shift said connections at will to encipher said code combinations by transposing the order in which the pulses are transmitted, means to further encipher said code combinations including devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each code combination before it is transmitted, means causing any desired one of said devices to reverse the pulse controlled by it in all of a number of successive code combinations, thereby enciphering a message or part thereof in one form, means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession to cause another pulse reversal in a difierent number of successive code combinations, and means at a receiving station to restore the pulses of each received code combination to their original order and for restoring the reversed pulses to normal.

7. In a secrecy system, means to translate messages into combinations of impulses representing characters or other signals in accordance with the Baudot code, said means including a transmitter having contacts individual to each pulse of a Baudot code combination and to which said pulses may be applied, conductors leading from a each of said contacts, a distributor having segments for each pulse of a code combination to successively transmit said pulses, conductors leading to each of said segments, a set of coordinate switching points arranged in rows extending in two directions, said conductors from the transmitter contacts leading to the switching points in each of the rows extending in one direction, said conductors leading to the segments of said distributor being associated one with each of the rows of switching points extending in the other direction, means at each switching point to connect the conductors leading from the transmitter contacts with the conductors leading to the seg' ments of the distributor in any desired order, means to further encipher said code combinations including devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each code combination before it is transmitted, means causing any desired one of said devices to reverse the pulse controlled by it in all of a number of successive code combinations, thereby enciphering a message or part thereof in one form; and means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession to cause another 16 pulse reversal in a different number of succes sive code combinations.

8. In a secrecy system, means to translate messages into combinations of impulses representing characters or other signals in accordance with the Baudot code, said means including a transmitter having contacts individual to each pulse of a Baudot code combination and to wh ch said pulses may be applied, conductors leadi g from each of said contacts, a distributor having segments for each pulse of a code combination to successively transmit said pulses, conductors leading to each of said segments, a set of coordinate switching points arranged in rows extending in two directions, said conductors from the transmitter contacts leading to the switching points in each of the rows extending in one direction, said conductors leading to the segments of said distributor being associated one with each of the rows of switching points extending in the other direction, means at each switching point to connect the conductors leading from the transmitter contacts with the conductors leading to the segments of the distributor in any desired order, means to further encipher said code combinations including devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each code combination before it is transmitted, means causing any desired one of said devices to reverse the pulse controlled by it in all of a number of successive code combinations,thereby enciphering a message or part thereof in one form, means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession to cause another pulse reversal in a difierent number of successive code combinations, and means at a receiving station to restore the pulses of each received code combination to their original order and for restoring the reversed pulses to normal.

ERNEST OSMOND GAMMELL. 

